Plant for recovering CO2 from a feed gas stream

Abstract

The invention relates to an installation (1) for recovering CO2 in a feed gas stream (FG), comprising: a unit (2) for processing the feed gas stream (FG) to produce, from the feed gas stream, a CO2-rich gas stream (FCO2) and a nitrogen-rich gas stream (FN), a compression stage (5) for compressing the feed gas stream (FG), an expansion stage (8) capable of delivering mechanical energy generated by the expansion of the nitrogen-rich gas stream, a thermal device (10) arranged to allow heat transfers between the gas stream leaving the compression stage (5) and the nitrogen-rich gas stream before expansion, a device (4) for recovering the mechanical energy delivered by the expansion stage. Abstract figure: Fig. 1

Description

Title of the invention: Installation for recovering CO2 from a feed gas stream

[0001] The present invention relates to an installation for recovering CO2 in a feed gas stream which is in particular combustion smoke.

[0002] Hydrogen is an energy vector that plays an increasing role in the decarbonization of various sectors, including transport and industry. Hydrogen can be produced from the natural gas reforming reaction (in SMR furnaces - "Steam Methane Reforming" or steam methane reforming). In SMR units, hydrogen production is accompanied by a significant production of CO2. A PSA type CO2 capture unit (which is a pressure swing adsorption device, or in English "Pressure Swing Adsorption") can be added to an SMR in order to reduce the carbon footprint of hydrogen production by SMR. CO2 capture (e.g. CO2 treatment and liquefaction for food use or for sequestration) can be carried out cryogenically or non-cryogenically, for example, amine washing. A high-pressure nitrogen-rich gas stream is produced at this time in the PSA unit.

[0003] The invention proposes to improve the energy efficiency of the installation.

[0004] The invention thus relates to an installation for recovering CO2 in a feed gas flow which is in particular combustion smoke, this installation comprising:

[0005] - a unit for treating the feed gas stream, by pressure modulation adsorption to produce, from the feed gas stream, a CO2-rich gas stream and a nitrogen-rich gas stream, - a compression assembly comprising at least one compression stage for compressing the feed gas flow before it enters the treatment unit, - a turbine comprising at least one expansion stage capable of delivering mechanical energy generated by the expansion of the nitrogen-rich gas flow in this expansion stage, - a thermal device arranged to allow heat transfers between the feed gas flow leaving a compression stage and the nitrogen-rich gas flow before expansion in the expansion stage, so as to heat the nitrogen-rich gas flow prior to its expansion, - a device for recovering the mechanical energy delivered by the expansion stage.

[0006] The feed gas stream, upstream of the compression assembly, may, for example, contain from 10% to 60% mol of CO2, in particular from 15% to 50% mol of CO2. The remainder is mainly nitrogen and small quantities of O2. Potentially argon Ar may be present with an order of magnitude of 1% mol or less, as well as traces of impurities, in particular NOx.

[0007] The feed gas stream may come from an SMR reformer, a cement plant, an oxycombustion unit, or a lime plant for example.

[0008] The feed gas stream may have undergone pre-treatment before entering the plant, for example through an amine scrubbing unit or a filtration unit.

[0009] The nitrogen-rich gas stream leaving the high-pressure PSA unit may contain, in addition to nitrogen, the least adsorbable constituents such as, where appropriate, O2, Ar, NO.

[0010] The percentage of nitrogen in the nitrogen-rich flow is notably between 50% and 90% volumetric.

[0011] CO2 represents a share of, for example, 50% to 85% volumetrically in the CO2-rich gas flow.

[0012] Generally, the compositions are given on a dry basis, that is to say, the water (H2O) is removed from the composition of the gas and the remaining constituents are standardized to 100.

[0013] According to one aspect of the invention, the feed gas flow arrives at the treatment unit, after having been compressed in the compression assembly, at a pressure in a range of 3 to 15 bar abs, in particular 6 to 12 bar abs, in particular 8 to 10 bar abs, and at a temperature close to ambient, for example between 5 and 45°C.

[0014] According to one aspect of the invention, the nitrogen-rich gas flow is discharged from the treatment unit at high pressure, in particular at a pressure of between 8 and 10 bars.

[0015] According to one aspect of the invention, the compression assembly comprises a centrifugal compressor in which the feed gas flow can be accelerated through one or more wheels rotated by a motor, in particular an electric motor. The energy thus acquired by the gas flow is transformed into an increase in its static pressure in a diffuser located at the outlet of each of the wheels. The arrangement of the wheels of the compression assembly depends on characteristics of the process, for example the flow rate, the compression ratio, the composition of the gas, but also on the technology specific to the different compressor manufacturers.

[0016] Generally, the motor drives a main rotation axis associated with a main gear and possibly an auxiliary gear. These gears are linked mechanically to pinions coupled to secondary rotation shafts. Each gear can thus drive several pinions. The respective dimensions of the gear and pinion determine the rotation speed of the secondary shaft depending on the rotation speed of the motor.

[0017] In the case where there is a single compression stage, the secondary axis drives the single wheel allowing the gas flow to be compressed to the chosen pressure.

[0018] When the compression assembly comprises several wheels to achieve the chosen overall compression ratio, that is to say the ratio of the outlet pressure to the inlet pressure in the compression assembly, there are different possible arrangements for these wheels.

[0019] It is also noted that, in the case where the compression is carried out in several stages, a compression ratio is defined per stage, i.e. the ratio of the outlet pressure of the stage in question to its inlet pressure.

[0020] It is also noted that, in this case, it is possible to partly adjust the respective compression ratios of the different stages in order to obtain the overall compression ratio, while remaining within the limits of possible dimensions, in particular while respecting the maximum permissible speeds and temperatures. This flexibility can make it easier to integrate the various compression wheels into the compression assembly.

[0021] The invention provides for associating with the compression assembly, one or more wheels of an expansion turbine in order to recover the mechanical energy produced by the expansion of the nitrogen-rich gas flow, which makes it possible to reduce the energy that the engine must provide.

[0022] In the present invention, the turbine, also called an expansion turbine, is equipment allowing the expansion of a fluid from its high pressure to its low pressure, the ratio of these pressures being called the expansion rate.

[0023] A turbine comprises one or more expansion stages, the number of expansion stages depending on the operating conditions, in particular the expansion rate.

[0024] In the case where the expansion is carried out in several stages, an expansion rate is also defined per stage, that is to say in this case, the ratio of inlet pressure to outlet pressure of the stage in question.

[0025] The expansion of the gas is carried out, in a very general way, through one or more wheels set in rotation by the gas and slowed down by a brake. In practice, the turbine can then comprise several wheels in series on the gas flow, each of the wheels being able to have its own geometry and its own rotation speed.

[0026] According to one aspect of the invention, the recovery device is an electrical generator capable of using the mechanical energy delivered by the expansion stage to produce electricity.

[0027] This electric generator makes it possible to use the relaxation energy by producing electricity which can be used locally or via an electrical network.

[0028] Alternatively, the recovery device comprises the compression stage which is arranged to receive mechanical energy delivered by the expansion stage.

[0029] In this case, the invention can make it possible to transmit the energy supplied by the turbine directly in mechanical form to the compression assembly of the installation.

[0030] It generally proves to be more advantageous from an economic point of view to modify a compressor by adding expansion wheels than to install an electric generator.

[0031] It will be noted that, in this type of expansion, the expanded gas is greatly cooled and that this can generate a risk of condensation in the wheel or at the outlet, leading to erosion problems, or even corrosion problems in the presence of constituents such as NOx.

[0032] Heating the nitrogen-rich gas flow before expansion makes it possible both to increase the recoverable energy and to avoid excessively low temperatures at the outlet of the expansion wheel(s).

[0033] In the case where there are several expansion stages, the expansion ratios of each stage can be varied in order to obtain the overall expansion ratio, while remaining within the limits of possible dimensions, in particular while respecting the maximum permissible peripheral speed. This flexibility can make it easier to add the expansion wheels to the compression assembly.

[0034] A turbine expansion wheel can have different positions:

[0035] - either on the same axis as a compression stage, preferably arranged on the other side of a pinion. It will be noted that, in this case, the turbine wheel and the compressor wheel rotate at the same speed. However, the internal speeds of the gas in the wheels, in particular the peripheral speeds, will depend on the geometry of each of the wheels. - or on a second axis still mechanically connected to a main gear but via a second pinion. In this case, the rotational speed of the turbine wheel is independent of the rotational speed of the compression wheel and depends only on the respective diameters of the main gear and the second pinion. It should be noted that the main gear can be mechanically connected to several pinions of different diameters, thus rotating several axes, each at a selected speed. - or on another axis mechanically connected to the secondary gear via another pinion. The speed of the detent wheel is then adaptable. - or possibly on an axle comprising a secondary pinion mechanically connected to the pinion driving a compression stage. Here too, The speed of the expansion wheel is adaptable according to the choice of the diameter of the secondary pinion. In this case, the compression stage receives torque from both the engine and the expansion wheel.

[0036] It can be seen that, depending on the configuration chosen, the energy produced by the expansion of the nitrogen-rich gas flow is directly transmitted to the rotation axis of the compression stage or to the main axis of the engine, so as to provide the energy of the expansion to the compression assembly.

[0037] The secondary gear can be arranged in any way on the motor axis, that is to say on the same side of the motor as the main gear or on the other side of the motor on an extension of the axis. It can be located between the motor and the main gear or after the main gear for example.

[0038] Two turbine wheels may possibly be on the same axis and be mechanically linked to the engine axis via a pinion in contact with the main gear or with the secondary gear or to the axis of a compression wheel.

[0039] As before, the energy of the expansion is supplied directly to the rotation axis of the compression wheel or to the engine axis. Thus the energy released by the expansions is supplied to the compression assembly.

[0040] In the case where the installation comprises at least two compression stages in the compression assembly and a turbine comprising at least two expansion stages actuable by the nitrogen-rich gas flow, the compression and expansion ratios respectively of at least one of the compression stages and of at least one expansion stage are chosen so that the compression wheel of the compression stage and the expansion wheel of the expansion stage have the same rotation speed and are mounted on the same axis.

[0041] In the case where the installation comprises a turbine comprising at least two expansion stages actuated by the nitrogen-rich gas flow, the respective expansion rates of the two expansion stages are chosen so that the corresponding wheels have the same rotation speed and are mounted on the same axis.

[0042] In the invention, there occurs, in the expansion stage(s) of the turbine, an expansion from a high pressure to a lower pressure of the nitrogen-rich gas flow, expansion which has the effect of setting into rotation, for example, a wheel of the turbine which is braked by the recovery device, which is for example the compression assembly. The invention thus makes it possible to improve the efficiency of the installation due to the recovery of mechanical energy from the nitrogen-rich gas flow, this flow being at high pressure and making it possible to actuate the expansion stage(s) of the turbine. The efficiency is notably improved compared to the case where the pressurized nitrogen flow would simply be discharged into the atmosphere, without being subject to energy recovery.

[0043] In the invention, the nitrogen flow, once expansion has been completed, is discharged into the atmosphere.

[0044] According to one aspect of the invention, the number of expansion stages of the turbine is adjusted according to requirements.

[0045] According to one aspect of the invention, the turbine expansion stage and the compression stage each comprise a rotating shaft and their shafts are connected such that rotation of the turbine expansion stage shaft provides torque to the compression stage shaft.

[0046] According to one aspect of the invention, the installation comprises at least two compression stages in the compression assembly and a turbine comprising at least two expansion stages actuable by the nitrogen-rich gas flow, each expansion stage of the turbine being arranged to transmit mechanical energy to the compression assembly, in particular whether directly to one of the compression stages or to a rotation shaft common to several compression stages or to a shaft of a motor which actuates the compression stages.

[0047] According to one aspect of the invention, the installation comprises at least two compression stages in the compression assembly and at least two expansion stages in which the nitrogen-rich gas flow expands, these expansion stages being arranged to deliver mechanical energy to the compression stages.

[0048] According to one aspect of the invention, these expansion stages are arranged in series so that the nitrogen-rich gas flow first passes through one of the expansion stages and then the other.

[0049] According to one aspect of the invention, each expansion stage is arranged to transmit mechanical energy to one of the compression stages.

[0050] According to one aspect of the invention, the expansion stage(s) transforming the energy of the nitrogen-rich gas flow may be sized to provide at least 25%, in particular approximately 40% or 50%, of the mechanical energy required to operate the compression stages.

[0051] The invention is thus particularly advantageous because it makes it possible to recycle energy and reduce the consumption of energy external to the installation.

[0052] During their passage through the thermal device, the nitrogen-rich gas flow, before expansion in the expansion stage, is for example at ambient temperature, and the feed gas flow leaving a compression stage is at a higher temperature.

[0053] The invention thus makes it possible to take advantage of the nitrogen-rich gas flow, which is substantially at ambient temperature at the outlet of the PSA unit, to cool the feed gas flow and heat the nitrogen-rich gas flow so as to improve the overall thermodynamic efficiency of the installation. Advantageously, the nitrogen cools the feed gas flow before compression, which makes this compression more efficient (because the volume to be compressed is smaller, the compression energy is lower) and, at the same time, the feed gas flow heats the nitrogen before expansion, making it possible to increase the recoverable energy.

[0054] According to one aspect of the invention, the thermal device comprises at least one gas / gas heat exchanger arranged to allow heat transfers between the feed gas flow leaving a compression stage and the nitrogen-rich gas flow before expansion in the expansion stage, so as to heat the nitrogen-rich gas flow prior to its expansion.

[0055] The invention makes it possible to prevent the nitrogen-rich flow from being at too low a temperature.

[0056] According to one aspect of the invention, the gas / gas heat exchanger is arranged at the outlet of the compression stage so that the feed gas flow first passes into the compression stage before passing through the heat exchanger.

[0057] The gas / gas heat exchanger thus makes it possible to cool the feed gas flow which has undergone an increase in temperature due to compression in the compression stage.

[0058] According to one aspect of the invention, the thermal device comprises at least two gas / gas heat exchangers for exchanging heat between the nitrogen-rich gas stream and the feed gas stream, each gas / gas heat exchanger being placed at the outlet of a compression stage.

[0059] According to one aspect of the invention, the two gas / gas heat exchangers are arranged in series for the nitrogen-rich gas flow so that this nitrogen-rich gas flow first passes through one of these gas / gas heat exchangers and then through the other of the gas / gas heat exchangers.

[0060] According to one aspect of the invention, an expansion stage of the turbine is provided downstream of each gas / gas heat exchanger so that the nitrogen-rich gas flow first passes into the gas / gas heat exchanger and then into the expansion stage which is used to transmit mechanical torque to the mechanical energy recovery device.

[0061] According to one aspect of the invention, the exchangers used, whether of the gas / gas type or of the gas / heat transfer fluid type, are tubular type exchangers with shell.

[0062] Depending on the flow rates, pressures and temperatures, these exchangers can also be plate exchangers.

[0063] According to one aspect of the invention, the nitrogen-rich gas flow passes several times through the same exchanger, for example a first time before expansion in the first expansion stage then, on leaving this expansion stage, a second time in the same exchanger before carrying out a second expansion in the second expansion stage. In this case, the exchanger is equivalent to two exchangers in parallel on the heat transfer fluid.

[0064] Such parallel exchanger configurations are described below, in connection with examples of implementation of the invention.

[0065] According to one aspect of the invention, the heat exchanges in the gas / gas exchangers are carried out by means of pairs of thermal regenerators, one of the regenerators of the pair accumulating the heat of the compressed feed gas flow while cooling it and the other restoring this heat to the nitrogen-rich gas flow while being cooled by this flow. The use of such a pair of thermal regenerators, instead of a gas / gas heat exchanger, is part of the invention.

[0066] According to one aspect of the invention, the thermal device comprises one or more gas / heat transfer fluid heat exchangers for exchanging heat between the feed gas flow and a heat transfer fluid other than the nitrogen-rich gas flow, this fluid being, for example, glycolated water belonging to a cooling circuit.

[0067] According to one aspect of the invention, the compression assembly comprises several compression stages, one or more gas / gas heat exchangers for exchanging heat between the nitrogen-rich gas stream and the feed gas stream and one or more gas / heat transfer fluid heat exchangers for exchanging heat between the feed gas stream and a cooling fluid other than the nitrogen-rich gas stream, each heat exchanger being arranged at the outlet of one of the compression stages so that the feed gas stream first passes into the compression stage before passing through the heat exchanger.

[0068] According to one aspect of the invention, all the compression stages are followed by a heat exchanger, either of the gas / gas type or of the gas / heat transfer fluid type.

[0069] Alternatively, at least one of the compression stages is directly connected to the following compression stage, without a heat exchanger between these two compression stages.

[0070] According to one aspect of the invention, the compression assembly comprises four compression stages, two stages each being followed by a gas / gas heat exchanger and two stages each being followed by a gas / heat transfer fluid heat exchanger.

[0071] According to one aspect of the invention, in the direction of circulation of the feed gas flow, the first two stages are each followed by a gas / heat transfer fluid heat exchanger and the last two stages are each followed by a gas / gas heat exchanger.

[0072] Thus the nitrogen-rich gas flow serves to cool the feed gas flow to the output of two compression stages.

[0073] According to one aspect of the invention, the turbine comprises two expansion stages and one of the expansion stages is placed downstream of one of the gas / gas heat exchangers and the other of the expansion stages is placed downstream of the other of the gas / gas heat exchangers.

[0074] According to one aspect of the invention, the expansion stages and the gas / gas heat exchangers are thus in series so that the nitrogen-rich gas flow passes successively into one of the gas / gas heat exchangers, then one of the expansion stages, then the other gas / gas heat exchanger and finally the other expansion stage.

[0075] According to one aspect of the invention, the nitrogen-rich gas flow is substantially at atmospheric pressure when it leaves the last expansion stage, and preferably at a temperature above -10°C, even more preferably above 0°C.

[0076] Such a temperature can be reached by sufficiently heating the nitrogen-rich gas flow and possibly by limiting the expansion rate of the turbine, for example with a valve placed on the nitrogen-rich gas flow circuit, preferably at the outlet of the last expansion stage.

[0077] This allows to avoid expensive materials, to avoid or minimize thermal insulation equipment and to make ice water.

[0078] Finally, the nitrogen-rich gas flow can be used for additional heat exchanges before being discharged into the atmosphere.

[0079] According to one aspect of the invention, one or more gas / heat transfer fluid heat exchangers may be provided downstream of the last gas / gas exchanger, so as to further cool the feed gas stream before it reaches the PSA treatment unit.

[0080] According to one aspect of the invention, a single gas / gas heat exchanger is provided in the installation, this exchanger being placed downstream of one of the compression stages.

[0081] Two expansion stages are arranged in series downstream of this heat exchanger so that the nitrogen-rich gas flow first passes into the gas / gas heat exchanger and then successively into the two expansion stages.

[0082] This can be advantageous if the expansion rate of the turbine from high pressure to low pressure is relatively low but nevertheless still too high to be achieved in a single expansion stage. It is then preferable to heat the inlet to the turbine as much as possible rather than providing two exchangers.

[0083] According to one aspect of the invention, one of the compression stages is directly connected to the following compression stage, for example the third compression stage is directly connected to a fourth compression stage, without a heat exchanger between these two compression stages.

[0084] According to one aspect of the invention, the installation comprises, for the gas flow rich in nitrogen, successively from the outlet of the treatment unit:

[0085] - a first gas / gas heat exchanger, - a first expansion stage, - a second gas / gas heat exchanger, - a second expansion stage, these first and second heat exchangers being placed, for the feed gas flow, in parallel with each other and downstream of a compression stage, in particular the first compression stage.

[0086] Thus, in this example, the nitrogen-rich gas flow is used to cool the feed gas flow in the two exchangers placed in parallel, at the outlet of the first compression stage.

[0087] According to one aspect of the invention, the feed gas flows subdivided in the two exchangers in parallel join at the outlet of these two exchangers to reform a single feed gas flow which passes into a gas / heat transfer fluid exchanger.

[0088] As can be seen, the feed gas stream sees two gas / gas exchangers as being in parallel, while the nitrogen-rich gas stream sees these two gas / gas exchangers as being in series.

[0089] According to one aspect of the invention, the installation comprises an intermediate thermal circuit using an intermediate heat transfer fluid separate from the nitrogen-rich gas flow and the feed gas flow, this intermediate circuit being arranged to allow heat exchanges between the nitrogen-rich gas flow and the feed gas flow via the intermediate heat transfer fluid.

[0090] According to one aspect of the invention, in the case where there are a plurality of compression stages, the nitrogen-rich gas flow is heated directly by a gas / gas exchanger, or indirectly by a gas / heat transfer fluid exchanger, via a heat transfer fluid, by taking heat from the feed gas flow leaving the compression stage having the highest temperature, preferably greater than 100°C, even more preferably greater than 120°C, this temperature having been obtained by ensuring that the compression stage in question has a higher compression ratio than the other stages or a higher inlet temperature.

[0091] According to one aspect of the invention, in the case where there are a plurality of compression stages, the nitrogen-rich gas flow is heated directly by a gas / gas exchanger, or indirectly by a gas / heat transfer fluid exchanger, via a heat transfer fluid, by taking heat from the feed gas flow leaving the compression stage having the highest temperature, preferably greater than 100°C, even more preferably greater than 120°C, this temperature having been obtained by ensuring that the compression stage in question has a compression ratio higher than the average of the compression ratios and / or an inlet temperature higher than the average of the inlet temperatures.

[0092] According to one aspect of the invention, at least twice this highest temperature level is used to reheat the nitrogen-rich gas stream before entering at least two expansion stages.

[0093] The invention thus makes it possible to take advantage of the highest temperature level of the feed gas flow to heat the nitrogen-rich gas flow as much as possible before each expansion stage.

[0094] Where appropriate, the nitrogen-rich gas stream heated by the feed gas stream via a gas / gas exchanger may be previously heated by one or more exchangers, in particular gas / heat transfer fluid, to carry out the first part of the heating and take maximum advantage of the highest temperature level.

[0095] According to one aspect of the invention, this intermediate circuit comprises a pump for circulating the intermediate fluid.

[0096] Conventionally, the installation may include instrumentation (temperature, pressure, vibration sensors, analyzers, etc.), valves (on / off valves, control valves, etc.) and ancillary equipment (filters, valves, bypass, etc.).

[0097] According to one aspect of the invention, the intermediate circuit is arranged so that the intermediate heat transfer fluid passes through at least one gas / heat transfer fluid heat exchanger to allow heat exchange between the heat transfer fluid and the feed gas stream and another gas / heat transfer fluid heat exchanger to allow heat exchange between the heat transfer fluid and the nitrogen-rich gas stream which is placed upstream of an expansion stage so that the nitrogen-rich gas stream passes through this exchanger to be heated by the intermediate heat transfer fluid before undergoing expansion in the expansion stage.

[0098] According to one aspect of the invention, the gas / heat transfer fluid heat exchanger to enable heat exchange between the heat transfer fluid and the feed gas flow is placed downstream of the first compression stage so that the feed gas flow is cooled by the intermediate fluid at the outlet of this first compression stage.

[0099] According to one aspect of the invention, the intermediate circuit is arranged to pass through two gas / heat transfer fluid heat exchangers to allow heat exchange between the heat transfer fluid and the nitrogen-rich gas flow, these exchangers each being placed upstream of an expansion stage.

[0100] According to one aspect of the invention, these two gas / heat transfer fluid heat exchangers allow heat exchange between the heat transfer fluid and the flow nitrogen-rich gaseous streams are placed in parallel for the intermediate heat transfer fluid so that this intermediate fluid is subdivided into two streams, each passing through one of these exchangers.

[0101] According to one aspect of the invention, the nitrogen-rich gas flow sees, for its part, a series arrangement of the gas / heat transfer fluid heat exchangers and the two expansion stages.

[0102] According to one aspect of the invention, the nitrogen-rich gas stream produced from the wet feed gas stream is dried before expansion in the expansion stage, so as to contain less than 50 ppm of H2O, preferably less than 5 ppm of H2O.

[0103] The invention also relates to a method for recovering CO2 in a feed gas stream which is in particular combustion smoke, this method comprising the following steps:

[0104] - compress, using a compression stage, the feed gas flow, - treat, using a treatment unit, the previously compressed feed gas flow, by pressure modulation adsorption to produce, from the feed gas flow, a CO2-rich gas flow at low pressure and a nitrogen-rich gas flow at high pressure, - use a turbine comprising at least one expansion stage capable of delivering mechanical energy generated by the expansion of the nitrogen-rich gas flow in this expansion stage, - allow heat transfers between the feed gas flow leaving the compression stage and the nitrogen-rich gas flow before expansion in the expansion stage, so as to heat the nitrogen-rich gas flow prior to its expansion, - use the mechanical energy delivered by the expansion stage, either to operate the compression assembly or to produce electricity using an electric generator.

[0105] According to one aspect of the invention, the fraction of the thermal compression energy is recovered by the nitrogen-rich gas flow by means of direct heat exchange with the feed gas flow at the outlet of at least one compression stage and / or by means of indirect heat exchange via a heat transfer fluid.

[0106] According to one aspect of the invention, the nitrogen-rich gas stream is reheated before being expanded through each of the expansion stages of the turbine.

[0107] According to one aspect of the invention, a torque transmission device is implemented between the respective shafts of the expansion stage(s) of the turbine and of the compression stage(s), this torque transmission device comprising in particular gears and pinions for transmitting a torque from the turbine to the compression assembly.

[0108] According to one aspect of the invention, the feed gas stream is wet and contains more than 10 ppm of NOx, the nitrogen-rich gas stream is dried before expansion so as to contain less than 50 ppm of H2O, preferably less than 5 ppm of H2O.

[0109] This makes it possible to avoid any possibility of condensation during the cooling caused by the expansion, and of the formation of nitric acid.

[0110] According to one aspect of the invention, the drying of the nitrogen-rich gas stream is carried out in the feed gas treatment unit by means of a hydrophilic adsorbent.

[0111] The invention can make it possible to take advantage of the fact that nitrogen is dry to make iced water.

[0112] The CO2-rich gas from the PSA unit may, if necessary, undergo additional treatments, including, for example, additional enrichment in CO2. The residual nitrogen then extracted from the CO2-rich gas can be recycled and used in expansion and energy recovery.

[0113] The invention will be better understood upon reading the following description and examining the accompanying figures. These figures are given only for illustrative purposes but in no way limit the invention.

[0114] [Fig. 1] [Fig. 1] is a schematic and partial representation of an installation according to a first example of the invention;

[0115] [Fig.2] [Fig.2] is a schematic and partial representation of an installation according to a second example of the invention;

[0116] [Fig.3] [Fig.3] is a schematic and partial representation of an installation according to a third example of the invention;

[0117] [Fig.4] [Fig.4] is a schematic and partial representation of an installation according to a fourth example of the invention.

[0118] [Fig.5] [Fig.5] is a schematic and partial representation of an installation according to a fifth example of the invention.

[0119] [Fig.l] shows an installation 1 for recovering CO2 in a feed gas flow FG which is, in the example described, a combustion flue gas, this installation comprising:

[0120] - a unit 2 for processing the feed gas flow FG, by pressure modulation adsorption (unit 2 being a PSA unit) to produce, from the feed gas flow, a CO2-rich gas flow called FCO2, and a nitrogen-rich gas flow called FN, - a compression assembly 3 comprising at least one compression stage 5 for compressing the feed gas flow FG before it enters the treatment unit 2, - a turbine 6 comprising at least one expansion stage 8 capable of delivering mechanical energy generated by the expansion of the nitrogen-rich gas flow FN in this expansion stage 8, - a thermal device 10 arranged to allow heat transfers between the feed gas flow FG leaving a compression stage 5 and the nitrogen-rich gas flow FN before expansion in the expansion stage 8, so as to heat the nitrogen-rich gas flow FN prior to its expansion, - a device 4 for recovering the mechanical energy delivered by the expansion stage 8.

[0121] The feed gas stream FG, upstream of the compression assembly 3, may, for example, contain from 10% to 60% mol of CO2, in particular from 15% to 50% mol of CO2. The remainder is mainly nitrogen and small quantities of O2. Potentially argon Ar may be present with an order of magnitude of 1% mol or less, as well as traces of impurities, in particular NOx.

[0122] The FG feed gas stream may come from an SMR reformer, a cement plant, an oxycombustion unit, or a lime plant.

[0123] The feed gas stream FG may have undergone pre-treatment before entering the installation, for example through a washing unit or a filtration unit.

[0124] The nitrogen-rich gas flow FN leaving the high-pressure unit 2 may contain, in addition to nitrogen, the least adsorbable constituents such as, where appropriate, O2, Ar, NO.

[0125] The percentage of nitrogen in the nitrogen-rich flow FN is notably between 50% and 90% volumetric.

[0126] CO2 represents a share of, for example, 50% to 85% volumetrically in the CO2-rich FCO2 gas flow.

[0127] Generally, the compositions are given on a dry basis.

[0128] The feed gas flow FG arrives at the treatment unit 2, after having been compressed in the compression assembly 3, at a pressure in a range of 8 to 10 bar abs, and at a temperature close to ambient, for example between 5 and 45°C.

[0129] The nitrogen-rich gas flow FN is discharged from the treatment unit 2 at high pressure, here at a pressure of between 8 and 10 bars.

[0130] The installation 1 comprises an electric motor 20 having an axis of rotation or shaft 21 secured to a main gear 22.

[0131] The installation 1 further comprises a pinion 23 driving a wheel of the compression stage 5 via a rotation axis or shaft 24.

[0132] Another pinion 25 in connection with the main gear 22 is arranged to transmit the rotational torque generated by the wheel of the expansion stage 8 of the turbine 6, via the rotational axis 26.

[0133] After compression, the feed gas flow FG is separated in the treatment unit 2. The nitrogen-rich gas flow FN, dry and under pressure, is reheated in the thermal device 10.

[0134] The expansion stage 8 transmits the energy from the expansion to the low pressure of the hot and pressurized gas FN in the turbine 6 to the main gear 22 and thus to the compression assembly 3.

[0135] Thus, the energy required by the compression stage 5 is supplied partly by the engine 20 and partly by the expansion turbine 6. Such an arrangement can very significantly reduce, for example by half, the electrical energy consumed by the engine 20.

[0136] In the example described, the recovery device 4 comprises the compression stage 5 which is arranged to receive mechanical energy delivered by the expansion stage 8, as well as the pinion 25 and the rotation axis 26 which ensure the transmission of the rotation torque.

[0137] Of course, various connections are possible between the wheels of the compression stage(s) and the expansion stage(s).

[0138] [Fig.2] illustrates an exemplary embodiment of the invention in the compression assembly 3 with four compression stages 5 and the turbine 6 has two expansion stages 8.

[0139] These expansion stages 8, each provided with a wheel, are arranged in series so that the nitrogen-rich gas flow FN first passes through one of the expansion stages 8 and then the other.

[0140] The expansion stages 8 transforming the energy of the nitrogen-rich gas flow FN can provide approximately 40% of the energy required to operate the compression stages.

[0141] In the example illustrated in [Fig.2], the thermal device 10 is arranged to allow heat transfers between the nitrogen-rich gas flow FN and the feed gas flow FG.

[0142] The nitrogen-rich gas stream FN is for example at ambient temperature, and the feed gas stream FG is at a higher temperature.

[0143] The invention thus makes it possible to take advantage of the nitrogen-rich gas flow FN, which is substantially at ambient temperature at the outlet of the PSA unit, to cool the feed gas flow FG so as to improve the overall thermodynamic efficiency of the installation 1.

[0144] The thermal device 10 comprises two gas / gas exchangers 11 in the compression assembly 3 and arranged to allow a heat exchange between the nitrogen-rich gas flow FN and the feed gas flow FG, to heat the nitrogen-rich gas flow FN and cool the feed gas flow FG.

[0145] Each gas / gas heat exchanger 11 for exchanging heat between the nitrogen-rich gas stream FN and the feed gas stream FG is arranged at the outlet of one of the compression stages 5 so that the feed gas stream FG first passes through the compression stage 5 before passing through the heat exchanger 11.

[0146] The gas / gas exchanger 11 thus makes it possible to cool the feed gas flow FG which has undergone an increase in temperature due to compression in the compression stage 5.

[0147] The two gas / gas exchangers 11 are arranged in series so that the nitrogen-rich gas flow FN first passes into one of these gas / gas exchangers 11 and then into the other of the gas / gas exchangers IL.

[0148] Each of the expansion stages 8 is provided downstream of each gas / gas heat exchanger 11 so that the nitrogen-rich gas flow FN first passes into the gas / gas heat exchanger 11 and then into the expansion stage 8 which serves to transmit mechanical torque to the dedicated compression stage 5.

[0149] The compression assembly 3 comprises three gas / heat transfer fluid heat exchangers 12 for exchanging heat between the feed gas flow FG and a cooling fluid other than the nitrogen-rich gas flow, this fluid here being glycolated water belonging to a cooling circuit.

[0150] Each heat exchanger 11 or 12 is arranged at the outlet of one of the compression stages 5 so that the feed gas flow FG first passes into the compression stage 5 before passing through the heat exchanger 11 or 12.

[0151] In the example of [Fig.2], all the compression stages 5 are followed by a heat exchanger, either of the gas / gas type 11 or of the gas / heat transfer fluid type 12.

[0152] In the direction of circulation of the feed gas flow FG, the first two compression stages 5, which are stages number 1 and number 2, are each followed by a gas / heat transfer fluid heat exchanger 12.

[0153] The last two stages 5 are each followed by a gas / gas heat exchanger 11.

[0154] Thus the nitrogen-rich gas flow FN serves to cool the feed gas flow FG at the outlet of two compression stages 5, which are stages number 3 and number 4.

[0155] The last gas / heat transfer fluid exchanger 12 is placed downstream of the last gas / gas exchanger 11 so as to further cool the feed gas flow before it reaches the PSA treatment unit.

[0156] The nitrogen-rich gas flow is, for its part, heated via the exchangers 11 by the feed fluid FG.

[0157] Each turbine stage 8 is placed downstream of one of the gas / gas exchangers 11.

[0158] The expansion stages 8 and the two gas / gas exchangers 11 are thus in series so that that the nitrogen-rich gas flow FN passes successively through one of the gas / gas exchangers 11, then one of the expansion stages 8, then the other gas / gas exchanger 11 and finally the other expansion stage 8.

[0159] The nitrogen-rich gas flow FN is substantially at atmospheric pressure when it leaves the last turbine 6, and preferably at a temperature above -10°C, even more preferably above 0°C.

[0160] In a variant illustrated in [Fig.3], one of the compression stages 5 is directly connected to the following compression stage 5, without a heat exchanger 11 or 12 between these two compression stages 5. Two expansion stages 8 are provided, as in the example of [Fig.2].

[0161] In the example of [Fig.3], a single gas / gas heat exchanger 11 is provided in the installation 1, this exchanger 11 being placed downstream of the last of the four compression stages 5.

[0162] Thus the nitrogen-rich gas flow FN first passes into the heat exchanger 11 and then successively into the two turbines 6.

[0163] In the example illustrated in [Fig.4], the installation 30 comprises, for the nitrogen-rich gas flow FN, successively from the outlet of the treatment unit:

[0164] - a first gas / gas heat exchanger 31, - a first expansion stage 33, - a second gas / gas heat exchanger 32, - a second expansion stage 34, - the first and second gas / gas heat exchangers 31 and 32 being placed, for the feed gas flow FG, in parallel with each other and downstream of the first of the four compression stages 5.

[0165] Thus, in this example, the nitrogen-rich gas flow FN is used to cool the feed gas flow FG in the two exchangers 31 and 32 placed in parallel, at the outlet of the first compression stage 5.

[0166] The feed gas flows FG subdivided into two branches 41 and 42 in the two exchangers 31 and 32 in parallel join at the outlet of these two exchangers 31 and 32 to reform a single feed gas flow FG which passes into a gas / heat transfer fluid exchanger 12.

[0167] As can be seen, the feed gas flow FG sees the two gas / gas exchangers 31 and 32 as being in parallel, whereas the nitrogen-rich gas flow FN sees these two gas / gas exchangers 31 and 32 as being in series.

[0168] The compression stages 5 are arranged to bring the feed gas flow FG from a pressure slightly lower than atmospheric pressure to approximately 8 or 9 bar abs which is the operating pressure of the PSA unit.

[0169] On a dry basis, the feed gas stream contains 22 mol% CO2, 75% molar N2, 2 molar O2, 1 molar Ar as well as impurities at a level of a few tens of ppm. The temperature is around 60°C, thus avoiding the condensation of liquid water.

[0170] The compression assembly 3 comprises an electric motor, not shown, actuating the four compression stages 5 in series. The expansion stages 8 of the turbine 6, also in series, provide a portion of the energy required for compression in the compression assembly 3. In the present case, the wheels of the expansion stages 8 provide approximately 40% of this energy.

[0171] The gas expanded in the expansion stages 8 is the high-pressure stream from the PSA unit. It contains 94 mol% N2, 3 mol% CO2, 2 mol% O2, 1 mol% Ar. This gas is available at approximately 8 bar abs and is expanded to a pressure slightly above atmospheric pressure. In order to increase the energy recoverable during expansion, this stream is reheated before entering each of the expansion stages to a temperature of 70 to 80°C. The corresponding heat is recovered from the feed gas stream FG leaving the first compression stage 5.

[0172] The inter-stage pressures of the compression assembly 5 are of the order of 2 bar abs (stage 1 outlet), 3.5 bar abs (stage 2 outlet), 5.5 bar abs (stage 3 outlet). The inter-stage pressure of expansion 8 is 3 bar abs. Similarly, the outlet temperatures of the compression stages are respectively of the order of 140 to 150°C (stage 1 outlet), and 75 to 85°C for the following stages. The exhaust temperatures of the expansion stages 8 are around 0°C.

[0173] The pressure staging, and more generally the operating conditions, are chosen such that the wheels of one stage of the compression assembly and of the second expansion stage 8 have the same rotation speed. Thus, these two wheels can have the same axis of rotation, for example on either side of a pinion.

[0174] The same may apply to the first expansion stage and another compression stage.

[0175] At the thermal level, the feed gas flow leaving the first compression stage 5 is first cooled by exchange with the nitrogen-rich flow FN. These exchanges are carried out by means of two gas-gas exchangers 31 and 32 which are U-tube, in parallel on the feed gas flow FG substantially divided in half between the two exchangers 31 and 32.

[0176] At the outlet of these exchangers 31 and 32, the feed gas flow is cooled to room temperature by cooling water, separated from the condensation water and is directed to the second compression stage 5. At the outlet of each stage 5, the feed gas flow is then cooled to room temperature by cooling water, separated from any condensation water.

[0177] It will be noted that the feed gas flow FG at the highest temperature is used to heat the inlet of the expansion stages 8, this makes it possible to increase the recoverable energy.

[0178] In the embodiment of [Fig.5], the installation 50 comprises an intermediate thermal circuit 51 using an intermediate heat transfer fluid separate from the nitrogen-rich gas flow FN and the feed gas flow FCO2, this intermediate circuit 51 being arranged to allow heat exchanges between the nitrogen-rich gas flow FN and the feed gas flow FCO2 via the intermediate heat transfer fluid.

[0179] This intermediate circuit 51 comprises a pump 52 for circulating the intermediate fluid. A temperature sensor 53 may be provided on this intermediate circuit 51.

[0180] The intermediate circuit 51 is arranged so that the intermediate heat transfer fluid passes into a gas / heat transfer fluid heat exchanger 55 arranged to allow heat exchanges between the intermediate heat transfer fluid of the circuit 51 and the feed gas flow FG, and two other gas / heat transfer fluid heat exchangers 56 which are each placed upstream of an expansion stage 8 so that the nitrogen-rich gas flow FN passes into this exchanger 56 to be heated by the heat transfer fluid of the circuit 51 before undergoing expansion in the expansion stages 8.

[0181] The gas / heat transfer fluid heat exchanger 55 for cooling the feed gas flow FG is placed downstream of the first compression stage 5 so that the feed gas flow FG is cooled by the intermediate fluid at the outlet of this first compression stage 5.

[0182] The two exchangers 56 are placed in parallel for the intermediate fluid so that the intermediate fluid is subdivided into two streams 61 and 62 each passing through one of these exchangers 56.

[0183] The nitrogen-rich gas flow FN sees, for its part, a series arrangement of the exchangers 56 and the expansion stages 8. Each expansion stage 8 is placed downstream of one of the exchangers 56.

[0184] In the installations which have just been described, a unit 65 is provided for producing chilled water using dry nitrogen from the stream FN. The chilled water stream 66 from the unit 65 is used in a heat exchanger 67 to further cool the gas stream FG which enters the PSA unit. A pump 68 is provided to circulate the chilled water stream. The stream FN is finally discharged into the atmosphere at location 69.

[0185] The CO2-rich FCO2 gas stream from the PSA unit may, if necessary, undergo additional treatments, including, for example, additional enrichment in CO2. The residual nitrogen then extracted from the CO2-rich gas may be recycled and contribute to relaxation and energy recovery.

Claims

Claims

1. Installation (1) for recovering CO2 from a feed gas stream (FG) which is in particular combustion fumes, this installation comprising: - a treatment unit (2) for the feed gas stream (FG), by pressure modulation adsorption to produce, from the feed gas stream, a CO2-rich gas stream (FCO2) and a nitrogen-rich gas stream (FN), - a compression assembly (3) comprising at least one compression stage (5) for compressing the feed gas stream before it enters the treatment unit, - a turbine (6) comprising at least one expansion stage (8) capable of delivering mechanical energy generated by the expansion of the nitrogen-rich gas stream (FN) in this expansion stage,- a thermal device (10) arranged to allow heat transfers between the feed gas flow (FG) leaving a compression stage (5) and the nitrogen-rich gas flow (FN) before expansion in the expansion stage, so as to heat the nitrogen-rich gas flow (FN) prior to its expansion, - a device (4) for recovering the mechanical energy delivered by the expansion stage.,

2. Installation according to the preceding claim, in which the recovery device is an electric generator capable of using the mechanical energy delivered by the expansion stage to produce electricity.

3. Installation according to claim 1, in which the recovery device (4) comprises the compression stage (5) which is arranged to receive mechanical energy delivered by the expansion stage.

4. Installation according to the preceding claim, comprising at least two compression stages (5) in the compression assembly and a turbine comprising at least two expansion stages (6) actuable by the nitrogen-rich gas flow (FN), each expansion stage of the turbine being arranged to transmit mechanical energy to the compression assembly, in particular directly to one compression stages or to a rotating shaft common to several compression stages or to a shaft of a motor which drives the compression stages.

5. Installation according to the preceding claim, in which these expansion stages (8) are arranged in series so that the nitrogen-rich gas flow (FN) first passes through one expansion stage and then the other.

6. Installation according to one of claims 3 to 5, in which the expansion stage(s) (8) are sized to provide at least 25%, in particular approximately 40% or 50%, of the mechanical energy required to operate the compression stages (5).

7. Installation according to one of the preceding claims, in which the thermal device (10) comprises at least one gas / gas heat exchanger (11) arranged to allow heat transfers between the feed gas flow (FG) leaving a compression stage (5) and the nitrogen-rich gas flow (FN) before expansion in the expansion stage, so as to heat the nitrogen-rich gas flow (FN) prior to its expansion.

8. Installation according to the preceding claim, in which the gas / gas heat exchanger (11) is arranged at the outlet of the compression stage (5) so that the feed gas flow (FG) first passes through the compression stage (5) before passing through the heat exchanger (H).

9. Installation according to one of the preceding claims, in which the thermal device (10) comprises one or more gas / heat transfer fluid heat exchangers (12) for exchanging heat between the supply gas flow (FG) and a heat transfer fluid other than the nitrogen-rich gas flow, this fluid being for example glycolated water belonging to a cooling circuit.

10. Installation according to one of claims 8 and 9, in which the installation comprises, for the nitrogen-rich gas flow (FN), successively from the outlet of the treatment unit: - a first gas / gas heat exchanger (11), - a first expansion stage (8), - a second gas / gas heat exchanger (11), - a second expansion stage (8), the first and second heat exchangers being placed, for the flow feed gas (FG), in parallel with each other and downstream of a compression stage (5), in particular the first compression stage.

11. Installation according to one of the preceding claims, in which the installation comprises an intermediate thermal circuit (51) using an intermediate heat transfer fluid separate from the nitrogen-rich gas flow (FN) and the feed gas flow (FG), this intermediate circuit being arranged to allow heat exchanges between the nitrogen-rich gas flow and the feed gas flow via the intermediate heat transfer fluid.

12. Installation according to one of the preceding claims, in which the nitrogen-rich gas stream (FN) produced from the wet feed gas stream (FG) is dried before expansion in the expansion stage, so as to contain less than 50 ppm of H20, preferably less than 5 ppm of H2O.

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